Igneous carbonatite in the Muji area, Artux, Xinjiang, China: Evidence from geological and geochemical analyses.

Abstract: A special type of carbonate intrusion occurs in the northwest of the Muji Area, West Kunlun Mountains, Xinjiang. Xenoliths of country rocks occur in the intrusion and are in embayed intrusive contact with the country rocks, with their edges occurring as apophyses and dikes penetrating into the country rocks, suggesting that this type of carbonate rocks is actually igneous carbonatite. Geochemically, the carbonatite is characterized by enrichment in CaO and CO2 and depletion in SiO2, TiO2, K2O, Na2O, Al2O3, FeO, Fe2O3, MnO and P2O5, and have very low REE, trace element and total REE contents, low LREE/HREE ratios and higher δ18O and δ13C values, indicating a crustal origin; so it is notably different from the carbonatite of mantle-derived origin. According to the above-mentioned characteristics, the carbonatite is igneous carbonatite of crustal origin which formed by melting of marine sedimentary carbonate rocks due to the intrusion of mantle-derived magma.